The layout of a conventional sighting zoom is illustrated in FIG. 1. Optical devices, such as the sighting zoom shown in FIG. 1, are often used to aid the aiming of weapons, such as rifles, pistols, bows, etc. Typically, a sighting zoom includes an objective 102 which focuses the target on a first image plane 104. The image on the first image plane 104 is then magnified and relayed to the second image plane 110 through the zoom 106. The eyepiece 108 relays that image from the second image plane 110 to the eye of the operator.
Conventional sighting zooms typically include a reticle, which can include cross-hairs or any other shape suited to assist the operator in aiming the associated weapon. An aiming reticle can be introduced into the system at either the first image plane 104 or second image plane 110, such that it remains in focus to the eye when viewing the target. If the reticle is introduced in the second image plane 110, the target changes in size during zooming; however, the aiming reticle does not vary in size. This limits the amount of useful information that can be provided to the user by the aiming reticle.
In contrast, a sighting zoom with a reticle positioned at the first image plane 104 has very different characteristics. If the aiming reticle is introduced in the first image plane 104, the aiming reticle will scale in size with the target while varying the magnification of the sighting zoom. A sighting zoom according to this arrangement enables detailed aiming measurements with the aiming reticle in addition to allowing the user to use detailed grid patterns on the aiming reticle to estimate size of the target, correct for ballistic drop, and compensate for cross winds.
Conventional sighting zooms allow adjustment of the magnification of the sighting zoom through a marked power ring on the exterior of the scope. The operator manually adjusts the magnification of the scope through rotation of the power ring. This requires the operator to remove his or her eye from its position on the scope in order to select the appropriate magnification, thereby disengaging visual contact with the target.